freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/data-structures/create-a-set-class.md

id, title, challengeType, forumTopicId

id	title	challengeType	forumTopicId
8d1323c8c441eddfaeb5bdef	Create a Set Class	1	301632

Description

In this exercise we are going to create a class named Set to emulate an abstract data structure called "set". A set is like an array, but it cannot contain duplicate values. The typical use for a set is to simply check for the presence of an item. We can see how the ES6 Set object works in the example below:

const set1 = new Set([1, 2, 3, 5, 5, 2, 0]);
console.log(set1);
// output: {1, 2, 3, 5, 0}
console.log(set1.has(1));
// output: true
console.log(set1.has(6));
// output: false

First, we will create an add method that adds a value to our set collection as long as the value does not already exist in the set. Then we will create a remove method that removes a value from the set collection if it already exists. And finally, we will create a size method that returns the number of elements inside the set collection.

Instructions

Create an add method that adds a unique value to the set collection and returns true if the value was successfully added and false otherwise.

Create a remove method that accepts a value and checks if it exists in the set. If it does, then this method should remove it from the set collection, and return true. Otherwise, it should return false. Create a size method that returns the size of the set collection.

Tests

tests:
  - text: Your <code>Set</code> class should have an <code>add</code> method.
    testString: assert((function(){var test = new Set(); return (typeof test.add === 'function')}()));
  - text: Your <code>add</code> method should not add duplicate values.
    testString: assert((function(){var test = new Set(); test.add('a'); test.add('b'); test.add('a'); var vals = test.values(); return (vals[0] === 'a' && vals[1] === 'b' && vals.length === 2)}()));
  - text: Your <code>add</code> method should return <code>true</code> when a value has been successfully added.
    testString: assert((function(){var test = new Set(); var result = test.add('a'); return (result != undefined) && (result === true);}()));
  - text: Your <code>add</code> method should return <code>false</code> when a duplicate value is added.
    testString: assert((function(){var test = new Set(); test.add('a'); var result = test.add('a'); return (result != undefined) && (result === false);}()));
  - text: Your <code>Set</code> class should have a <code>remove</code> method.
    testString: assert((function(){var test = new Set(); return (typeof test.remove === 'function')}()));
  - text: Your <code>remove</code> method should only remove items that are present in the set.
    testString: assert.deepEqual((function(){var test = new Set(); test.add('a');test.add('b');test.remove('c'); return test.values(); })(), ['a', 'b']);
  - text: Your <code>remove</code> method should remove the given item from the set.
    testString: assert((function(){var test = new Set(); test.add('a');test.add('b');test.remove('a'); var vals = test.values(); return (vals[0] === 'b' && vals.length === 1)}()));
  - text: Your <code>Set</code> class should have a <code>size</code> method.
    testString: assert((function(){var test = new Set(); return (typeof test.size === 'function')}()));
  - text: The <code>size</code> method should return the number of elements in the collection.
    testString: assert((function(){var test = new Set(); test.add('a');test.add('b');test.remove('a');return (test.size() === 1)}()));

Challenge Seed

class Set {
  constructor() {
    // Dictionary will hold the items of our set
    this.dictionary = {};
    this.length = 0;
  }

  // This method will check for the presence of an element and return true or false
  has(element) {
    return this.dictionary[element] !== undefined;
  }

  // This method will return all the values in the set
  values() {
    return Object.keys(this.dictionary);
  }

  // Only change code below this line
  
  // Only change code above this line
}

Solution

class Set {
  constructor() {
    this.dictionary = {};
    this.length = 0;
  }

  has(element) {
    return this.dictionary[element] !== undefined;
  }

  values() {
    return Object.keys(this.dictionary);
  }

  add(element) {
    if (!this.has(element)) {
      this.dictionary[element] = true;
      this.length++;
      return true;
    }

    return false;
  }

  remove(element) {
    if (this.has(element)) {
      delete this.dictionary[element];
      this.length--;
      return true;
    }

    return false;
  }

  size() {
    return this.length;
  }
}